IDENTIFICATION OF HIGH-POTENCY NEUROPEPTIDE-Y ANALOGS THROUGH SYSTEMATIC LACTAMIZATION

In the pursuit of potent analogues of neuropeptide Y (NPY) that are se lective for the Y-1 receptor subtype, two lactam bridge scans of a cen trally truncated parent compound were synthesized. A single lactam bri dge (gamma-carboxyl of Glu to epsilon-amino of Lys) extending from res idues i to i + 3 or i to i + 4 of the proposed alpha-helical region (r esidues 25-31 of NPY) was introduced in des-AA(7-24)[Gly(6)]NPY. Cyclo gues (contraction of cyclic analogues), which were approximately one-h alf the size of native NPY, were initially screened for binding affini ty at two discrete NPY receptor types using human neuroblastoma cell m embranes, SK-N-MC and SK-N-BE2. Exploitation of the subtle differences present on each receptor type allowed for the identification of cyclo gues which bound specifically to Y-1 receptors with increased affinity when compared to the corresponding linear parent analogue, while one short Y-1 specific cyclogue, des-AA(2,3,5,7-24)cyclo- (26/29)[Gly(6),G lu(26),Lys(29),Pro(34)]NPY, bound with K-i = 16 nM. Other cyclogues sh owed distinct preference for Y-2 receptors and bound in the low-nanomo lar range. Functionally, the compounds inhibited the norepinephrine-st imulated accumulation of cAMP indicating that all acted as agonists wi th varying potencies.